Trunked radio systems, acting as stand-alone systems or as part of a wide geographic area coverage system, and having telephone interconnect capabilities assigned to specific radios within that radio system, are known. In the stand-alone configuration, subscribers may wish to dial land-line individuals who may be geographically located outside of the calling area, as defined by the calling code, or area code, associated with the Public Switched Telephone Network (PSTN) phone lines at the fixed site upon which the mobile is active. Currently, doing so requires the keyed entry of three or more characters, in addition to the PSTN telephone number of the land-line unit, in order to successfully complete the interconnect call.
For wide area systems with a multitude of fixed sites, each fixed site having a set of PSTN phone lines which are associated with a calling code. Some of these codes are common among different sites, while others are unique to that site. Users of subscriber units within the system will be assigned to a specific primary, or home, site and will more than likely be making interconnect calls within that primary site's area code. This radio user, however, has the ability to roam into another site's boundaries within the trunked radio system. Once the radio has moved into a new site away from its home site, the user may be required to enter the area code of the radio's home site if the user wishes to make a telephone interconnect call to a land-line within the area code boundaries of the radio's home site. This becomes a requirement when the site upon which the radio is active has a different area code than the land-line in its home site. Additionally, a radio user roaming between sites would normally be required to dial the area code of the radio's home site, if outside the boundaries of that site's area code. This radio user may roam from these boundaries quite often, but desire to make many calls to individuals located within the area code of the home site. In the case where a subscriber unit is continually roaming along area code boundaries, there may be a requirement to preface the area code of a desired land-line number for every call initiated by that subscriber unit.
There are two problems associated with the aforementioned scenario. The first, and perhaps most obvious, is the inconvenience associated with having to dial the area codes necessary for a given land-line interconnect call, in addition to the required seven digit number for that land-line. This condition, is merely a nuisance to the initiating party. The second problem goes beyond that, though. If either the area code is prefaced by the user to the seven digit number when it is not required to do so, or the area code is ignored by the user when its presence is required, the call initiation attempt will fail. This failure results in, at best, a requirement to reinitiate the call. In an emergency situation, of course, the consequences of the aforementioned scenario are more severe.
Accordingly, the need exists for a trunked communication system to have the capability of both determining whether or not a calling, or area code is required, and then if there is such a requirement, generating a number by prefacing the appropriate area code to the telephone number keyed by the user of the roaming subscriber unit.